Vacuum pump, spiral plate provided in vacuum pump, rotating cylinder and method for manufacturing spiral plate

Abstract

In a vacuum pump, a spiral plate on a downstream side of a slit is not disposed on an extended line of a spiral plate on an upstream side of the slit but is disposed after in a direction in which a gap formed by the slit is reduced. The distance by which the downstream spiral plate is moved corresponds to the distance in which the gap disappears and the upstream spiral plate and the downstream spiral plate overlap. When scraping the spiral plates, the radius of a machining end mill is set smaller than the width of the slit of the spiral plate, and the radius of the machining end mill is set smaller than the phase difference between the upstream spiral plate and the downstream spiral plate. In addition, end portions of the spiral plates between which the slit is formed are subjected to chamfering.

What is claimed is: 
     
       1. A vacuum pump, comprising:
 a housing in which an inlet port and an outlet port are formed; 
 a rotating shaft enclosed in the housing and supported rotatably; 
 spiral plates provided with at least one slit and disposed in a spiral form on an outer peripheral surface of the rotating shaft or of a rotating cylinder disposed on the rotating shaft; 
 a stator disc disposed in the slit of each of the spiral plates, with a predetermined space from the slit, and having a hole portion penetrating the stator disc; 
 a spacer for fixing the stator disc; and 
 a vacuum exhaust mechanism for transferring gas sucked from the inlet port to the outlet port by an interaction between the spiral plates and the stator disc, 
 wherein at least one of the spiral plates on a downstream side of the slit is disposed offset from an extended line of at least one of the spiral plates on an upstream side of the slit in a direction in which the spiral plate on the downstream side of the slit overlaps the spiral plate on the upstream side of the slit. 
 
     
     
       2. The vacuum pump according to  claim 1 , wherein the spiral plate on the upstream side and the spiral plate on the downstream side overlap each other with a predetermined gap therebetween in at least one of a plurality of the slits, and the slit becomes invisible in a direction of the rotating shaft. 
     
     
       3. The vacuum pump according to  claim 1 , wherein in at least one of a plurality of the slits, a phase difference between the spiral plate on the upstream side and the spiral plate on the downstream side is equivalent to a width of the slit. 
     
     
       4. The vacuum pump according to  claim 1 , wherein at least one of acute angle portions formed by dividing the spiral plates by the slit is subjected to chamfering. 
     
     
       5. The vacuum pump according to  claim 4 , wherein the chamfering is performed within a width of a horizontal plane formed by dividing the spiral plates by the slit, and the chamfer has an acute angle. 
     
     
       6. The vacuum pump according to  claim 1 , comprising the spiral plates cut by a cutting tool having a radius smaller than at least one of a width of the slit of each of the spiral plates and a phase difference between the spiral plate on the upstream side and the spiral plate on the downstream side. 
     
     
       7. A spiral plate which is provided in the vacuum pump according to  claim 1 . 
     
     
       8. A rotating cylinder, comprising the spiral plate according to  claim 7 . 
     
     
       9. A method for manufacturing the spiral plate according to  claim 7 , the method comprising:
 a first step of cutting an inclined surface of the spiral plate on the downstream side; 
 a second step of forming the chamfer on the spiral plate on the downstream side; and 
 a third step of cutting an inclined surface of the spiral plate on the upstream side. 
 
     
     
       10. The vacuum pump according to  claim 2 , wherein in at least one of a plurality of the slits, a phase difference between the spiral plate on the upstream side and the spiral plate on the downstream side is equivalent to a width of the slit. 
     
     
       11. The vacuum pump according to  claim 2 , wherein at least one of acute angle portions formed by dividing the spiral plates by the slit is subjected to chamfering. 
     
     
       12. The vacuum pump according to  claim 3 , wherein at least one of acute angle portions formed by dividing the spiral plates by the slit is subjected to chamfering. 
     
     
       13. The vacuum pump according to  claim 2 , comprising the spiral plates cut by a cutting tool having a radius smaller than at least one of a width of the slit of each of the spiral plates and a phase difference between the spiral plate on the upstream side and the spiral plate on the downstream side. 
     
     
       14. The vacuum pump according to  claim 3 , comprising the spiral plates cut by a cutting tool having a radius smaller than at least one of a width of the slit of each of the spiral plates and a phase difference between the spiral plate on the upstream side and the spiral plate on the downstream side. 
     
     
       15. The vacuum pump according to  claim 4 , comprising the spiral plates cut by a cutting tool having a radius smaller than at least one of a width of the slit of each of the spiral plates and a phase difference between the spiral plate on the upstream side and the spiral plate on the downstream side.